It can work. Best not used for serious or critical apps because very few manufacturers use the "feedback" capability (so you know what you asked for actually got done). Most pros will suggest hard-wiring when possible.

That said, I've used a X-10 photocontroller to turn on/off the outside lights around the house and a couple inside for more than 20 years, and I've never had to replace a single one of the units. OTOH, the modules I install in the wall (light and outlet switches) seem to go bad pretty often. I have mostly replaced them with regular switches/outlets after the second failure in each location. Oddly, some locations never seem to fail, and if anything it's the ones with a real light load (like one 60W bulb) that seem to fail the most (???). Some brands of X-10 stuff are better than others, they aren't all the same, even though they may look the same.

Also use the IR controller and the modular units you plug into outlets in my HT room for lights etc. Control with my regular HT IR remote. That is fine, you can see if the signal got through. I wouldn't trust these if I couldn't.

And I have some of the X-10 alarm units. They have been very reliable, not one has gone bad in over 20 years too. But this is a backup alarm now, I feed each sensor a 9V battery every couple years so it's not a big expense. I have the sensors in areas that aren't quite so critical and would have been expensive to hard-wire.

I have got some stuff from X10.com. It's true, they're a spam machine. And it's always big spam. But the stuff I got from them (PC interface, controllers etc.) all work fine for what it is. Price and service were fine too.

Hope this helps. If you are serious, pay the bigger $$ and use the X-10 stuff with feedback if appropriate for the job, it's a totally different quality league than what most people think of as X-10. I would not trust the regular stuff to run my home while I was away, say. With the feedback X-10, you could check/run your house over the web fairly reliably. I'm assuming this bidirectional X-10 stuff is still available, haven't bought any new stuff for quite a few years...